1. Technical Field
This application relates to tracking systems and, more particularly, to determining the spatial orientation of a moveable object.
2. Related Art
Many applications use surround sound techniques to enhance the quality of audio playback for listeners. The perception of surround sound reproduced from audio data may be based on the principles that listeners use to locate sound sources in space in every day life. Namely, sound signals from a particular sound source may arrive at the ears of a listener at different times and with other non-uniformities. Additionally, the human ear influences the frequency of incoming sound signals dependent on the direction of the incoming signal.
When a listener experiences surround sound from loudspeakers, the listener receives both direct sound from each loudspeaker and multiple reflections. By the time sound reaches the listener, the sound from each speaker has acquired a unique signature. These signatures cue the brain as to the size and acoustical properties of the room, the location of the loudspeakers, and the spatial properties of the original sound.
If, however, the listener experiences a surround sound reproduction through a headphone unit, then the effects of amplitude and phase shifting as well as frequency filtering may be eliminated. Without these effects, the listener may be unable to locate the position of various sound sources. Rather, the sound sources are located directly at both ears. Another drawback occurs in the situation where the head of a person turns while listening to simulated surround sound via headphones. The simulated sound field turns together with the head and seems the same to the listener regardless of the orientation of the listener's head. Therefore, the listener will not have a true surround sound experience.
Some systems attempt to overcome this drawback by tracking the movement of the head of the listener. These systems use head tracking information and additional pre-processing to reflect the movements of the head in the sound data fed to the headphones. Some head tracking systems include a measurement device. Others include transmitters. In both systems, a large amount of hardware may be required. Therefore, a need exists for an improved tracking system with a reduced hardware effort.